CREATE INDEX(7) PostgreSQL 15.7 Documentation CREATE INDEX(7)
NAME
CREATE_INDEX - define a new index
SYNOPSIS
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] name ] ON [ ONLY ] table_name [ USING method ]
( { column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ INCLUDE ( column_name [, ...] ) ]
[ NULLS [ NOT ] DISTINCT ]
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ TABLESPACE tablespace_name ]
[ WHERE predicate ]
DESCRIPTION
CREATE INDEX constructs an index on the specified column(s) of the
specified relation, which can be a table or a materialized view.
Indexes are primarily used to enhance database performance (though
inappropriate use can result in slower performance).
The key field(s) for the index are specified as column names, or
alternatively as expressions written in parentheses. Multiple fields
can be specified if the index method supports multicolumn indexes.
An index field can be an expression computed from the values of one or
more columns of the table row. This feature can be used to obtain fast
access to data based on some transformation of the basic data. For
example, an index computed on upper(col) would allow the clause WHERE
upper(col) = 'JIM' to use an index.
PostgreSQL provides the index methods B-tree, hash, GiST, SP-GiST, GIN,
and BRIN. Users can also define their own index methods, but that is
fairly complicated.
When the WHERE clause is present, a partial index is created. A partial
index is an index that contains entries for only a portion of a table,
usually a portion that is more useful for indexing than the rest of the
table. For example, if you have a table that contains both billed and
unbilled orders where the unbilled orders take up a small fraction of
the total table and yet that is an often used section, you can improve
performance by creating an index on just that portion. Another possible
application is to use WHERE with UNIQUE to enforce uniqueness over a
subset of a table. See Section 11.8 for more discussion.
The expression used in the WHERE clause can refer only to columns of
the underlying table, but it can use all columns, not just the ones
being indexed. Presently, subqueries and aggregate expressions are also
forbidden in WHERE. The same restrictions apply to index fields that
are expressions.
All functions and operators used in an index definition must be
“immutable”, that is, their results must depend only on their arguments
and never on any outside influence (such as the contents of another
table or the current time). This restriction ensures that the behavior
of the index is well-defined. To use a user-defined function in an
index expression or WHERE clause, remember to mark the function
immutable when you create it.
PARAMETERS
UNIQUE
Causes the system to check for duplicate values in the table when
the index is created (if data already exist) and each time data is
added. Attempts to insert or update data which would result in
duplicate entries will generate an error.
Additional restrictions apply when unique indexes are applied to
partitioned tables; see CREATE TABLE (CREATE_TABLE(7)).
CONCURRENTLY
When this option is used, PostgreSQL will build the index without
taking any locks that prevent concurrent inserts, updates, or
deletes on the table; whereas a standard index build locks out
writes (but not reads) on the table until it's done. There are
several caveats to be aware of when using this option — see
Building Indexes Concurrently below.
For temporary tables, CREATE INDEX is always non-concurrent, as no
other session can access them, and non-concurrent index creation is
cheaper.
IF NOT EXISTS
Do not throw an error if a relation with the same name already
exists. A notice is issued in this case. Note that there is no
guarantee that the existing index is anything like the one that
would have been created. Index name is required when IF NOT EXISTS
is specified.
INCLUDE
The optional INCLUDE clause specifies a list of columns which will
be included in the index as non-key columns. A non-key column
cannot be used in an index scan search qualification, and it is
disregarded for purposes of any uniqueness or exclusion constraint
enforced by the index. However, an index-only scan can return the
contents of non-key columns without having to visit the index's
table, since they are available directly from the index entry.
Thus, addition of non-key columns allows index-only scans to be
used for queries that otherwise could not use them.
It's wise to be conservative about adding non-key columns to an
index, especially wide columns. If an index tuple exceeds the
maximum size allowed for the index type, data insertion will fail.
In any case, non-key columns duplicate data from the index's table
and bloat the size of the index, thus potentially slowing searches.
Furthermore, B-tree deduplication is never used with indexes that
have a non-key column.
Columns listed in the INCLUDE clause don't need appropriate
operator classes; the clause can include columns whose data types
don't have operator classes defined for a given access method.
Expressions are not supported as included columns since they cannot
be used in index-only scans.
Currently, the B-tree, GiST and SP-GiST index access methods
support this feature. In these indexes, the values of columns
listed in the INCLUDE clause are included in leaf tuples which
correspond to heap tuples, but are not included in upper-level
index entries used for tree navigation.
name
The name of the index to be created. No schema name can be included
here; the index is always created in the same schema as its parent
table. The name of the index must be distinct from the name of any
other relation (table, sequence, index, view, materialized view, or
foreign table) in that schema. If the name is omitted, PostgreSQL
chooses a suitable name based on the parent table's name and the
indexed column name(s).
ONLY
Indicates not to recurse creating indexes on partitions, if the
table is partitioned. The default is to recurse.
table_name
The name (possibly schema-qualified) of the table to be indexed.
method
The name of the index method to be used. Choices are btree, hash,
gist, spgist, gin, brin, or user-installed access methods like
bloom. The default method is btree.
column_name
The name of a column of the table.
expression
An expression based on one or more columns of the table. The
expression usually must be written with surrounding parentheses, as
shown in the syntax. However, the parentheses can be omitted if the
expression has the form of a function call.
collation
The name of the collation to use for the index. By default, the
index uses the collation declared for the column to be indexed or
the result collation of the expression to be indexed. Indexes with
non-default collations can be useful for queries that involve
expressions using non-default collations.
opclass
The name of an operator class. See below for details.
opclass_parameter
The name of an operator class parameter. See below for details.
ASC
Specifies ascending sort order (which is the default).
DESC
Specifies descending sort order.
NULLS FIRST
Specifies that nulls sort before non-nulls. This is the default
when DESC is specified.
NULLS LAST
Specifies that nulls sort after non-nulls. This is the default when
DESC is not specified.
NULLS DISTINCT
NULLS NOT DISTINCT
Specifies whether for a unique index, null values should be
considered distinct (not equal). The default is that they are
distinct, so that a unique index could contain multiple null values
in a column.
storage_parameter
The name of an index-method-specific storage parameter. See Index
Storage Parameters below for details.
tablespace_name
The tablespace in which to create the index. If not specified,
default_tablespace is consulted, or temp_tablespaces for indexes on
temporary tables.
predicate
The constraint expression for a partial index.
Index Storage Parameters
The optional WITH clause specifies storage parameters for the index.
Each index method has its own set of allowed storage parameters. The
B-tree, hash, GiST and SP-GiST index methods all accept this parameter:
fillfactor (integer)
The fillfactor for an index is a percentage that determines how
full the index method will try to pack index pages. For B-trees,
leaf pages are filled to this percentage during initial index
builds, and also when extending the index at the right (adding new
largest key values). If pages subsequently become completely full,
they will be split, leading to fragmentation of the on-disk index
structure. B-trees use a default fillfactor of 90, but any integer
value from 10 to 100 can be selected.
B-tree indexes on tables where many inserts and/or updates are
anticipated can benefit from lower fillfactor settings at CREATE
INDEX time (following bulk loading into the table). Values in the
range of 50 - 90 can usefully “smooth out” the rate of page splits
during the early life of the B-tree index (lowering fillfactor like
this may even lower the absolute number of page splits, though this
effect is highly workload dependent). The B-tree bottom-up index
deletion technique described in Section 67.4.2 is dependent on
having some “extra” space on pages to store “extra” tuple versions,
and so can be affected by fillfactor (though the effect is usually
not significant).
In other specific cases it might be useful to increase fillfactor
to 100 at CREATE INDEX time as a way of maximizing space
utilization. You should only consider this when you are completely
sure that the table is static (i.e. that it will never be affected
by either inserts or updates). A fillfactor setting of 100
otherwise risks harming performance: even a few updates or inserts
will cause a sudden flood of page splits.
The other index methods use fillfactor in different but roughly
analogous ways; the default fillfactor varies between methods.
B-tree indexes additionally accept this parameter:
deduplicate_items (boolean)
Controls usage of the B-tree deduplication technique described in
Section 67.4.3. Set to ON or OFF to enable or disable the
optimization. (Alternative spellings of ON and OFF are allowed as
described in Section 20.1.) The default is ON.
Note
Turning deduplicate_items off via ALTER INDEX prevents future
insertions from triggering deduplication, but does not in
itself make existing posting list tuples use the standard tuple
representation.
GiST indexes additionally accept this parameter:
buffering (enum)
Determines whether the buffered build technique described in
Section 68.4.1 is used to build the index. With OFF buffering is
disabled, with ON it is enabled, and with AUTO it is initially
disabled, but is turned on on-the-fly once the index size reaches
effective_cache_size. The default is AUTO. Note that if sorted
build is possible, it will be used instead of buffered build unless
buffering=ON is specified.
GIN indexes accept different parameters:
fastupdate (boolean)
This setting controls usage of the fast update technique described
in Section 70.4.1. It is a Boolean parameter: ON enables fast
update, OFF disables it. The default is ON.
Note
Turning fastupdate off via ALTER INDEX prevents future
insertions from going into the list of pending index entries,
but does not in itself flush previous entries. You might want
to VACUUM the table or call gin_clean_pending_list function
afterward to ensure the pending list is emptied.
gin_pending_list_limit (integer)
Custom gin_pending_list_limit parameter. This value is specified in
kilobytes.
BRIN indexes accept different parameters:
pages_per_range (integer)
Defines the number of table blocks that make up one block range for
each entry of a BRIN index (see Section 71.1 for more details). The
default is 128.
autosummarize (boolean)
Defines whether a summarization run is queued for the previous page
range whenever an insertion is detected on the next one. See
Section 71.1.1 for more details. The default is off.
Building Indexes Concurrently
Creating an index can interfere with regular operation of a database.
Normally PostgreSQL locks the table to be indexed against writes and
performs the entire index build with a single scan of the table. Other
transactions can still read the table, but if they try to insert,
update, or delete rows in the table they will block until the index
build is finished. This could have a severe effect if the system is a
live production database. Very large tables can take many hours to be
indexed, and even for smaller tables, an index build can lock out
writers for periods that are unacceptably long for a production system.
PostgreSQL supports building indexes without locking out writes. This
method is invoked by specifying the CONCURRENTLY option of CREATE
INDEX. When this option is used, PostgreSQL must perform two scans of
the table, and in addition it must wait for all existing transactions
that could potentially modify or use the index to terminate. Thus this
method requires more total work than a standard index build and takes
significantly longer to complete. However, since it allows normal
operations to continue while the index is built, this method is useful
for adding new indexes in a production environment. Of course, the
extra CPU and I/O load imposed by the index creation might slow other
operations.
In a concurrent index build, the index is actually entered as an
“invalid” index into the system catalogs in one transaction, then two
table scans occur in two more transactions. Before each table scan, the
index build must wait for existing transactions that have modified the
table to terminate. After the second scan, the index build must wait
for any transactions that have a snapshot (see Chapter 13) predating
the second scan to terminate, including transactions used by any phase
of concurrent index builds on other tables, if the indexes involved are
partial or have columns that are not simple column references. Then
finally the index can be marked “valid” and ready for use, and the
CREATE INDEX command terminates. Even then, however, the index may not
be immediately usable for queries: in the worst case, it cannot be used
as long as transactions exist that predate the start of the index
build.
If a problem arises while scanning the table, such as a deadlock or a
uniqueness violation in a unique index, the CREATE INDEX command will
fail but leave behind an “invalid” index. This index will be ignored
for querying purposes because it might be incomplete; however it will
still consume update overhead. The psql \d command will report such an
index as INVALID:
postgres=# \d tab
Table "public.tab"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
col | integer | | |
Indexes:
"idx" btree (col) INVALID
The recommended recovery method in such cases is to drop the index and
try again to perform CREATE INDEX CONCURRENTLY. (Another possibility is
to rebuild the index with REINDEX INDEX CONCURRENTLY).
Another caveat when building a unique index concurrently is that the
uniqueness constraint is already being enforced against other
transactions when the second table scan begins. This means that
constraint violations could be reported in other queries prior to the
index becoming available for use, or even in cases where the index
build eventually fails. Also, if a failure does occur in the second
scan, the “invalid” index continues to enforce its uniqueness
constraint afterwards.
Concurrent builds of expression indexes and partial indexes are
supported. Errors occurring in the evaluation of these expressions
could cause behavior similar to that described above for unique
constraint violations.
Regular index builds permit other regular index builds on the same
table to occur simultaneously, but only one concurrent index build can
occur on a table at a time. In either case, schema modification of the
table is not allowed while the index is being built. Another difference
is that a regular CREATE INDEX command can be performed within a
transaction block, but CREATE INDEX CONCURRENTLY cannot.
Concurrent builds for indexes on partitioned tables are currently not
supported. However, you may concurrently build the index on each
partition individually and then finally create the partitioned index
non-concurrently in order to reduce the time where writes to the
partitioned table will be locked out. In this case, building the
partitioned index is a metadata only operation.
NOTES
See Chapter 11 for information about when indexes can be used, when
they are not used, and in which particular situations they can be
useful.
Currently, only the B-tree, GiST, GIN, and BRIN index methods support
multiple-key-column indexes. Whether there can be multiple key columns
is independent of whether INCLUDE columns can be added to the index.
Indexes can have up to 32 columns, including INCLUDE columns. (This
limit can be altered when building PostgreSQL.) Only B-tree currently
supports unique indexes.
An operator class with optional parameters can be specified for each
column of an index. The operator class identifies the operators to be
used by the index for that column. For example, a B-tree index on
four-byte integers would use the int4_ops class; this operator class
includes comparison functions for four-byte integers. In practice the
default operator class for the column's data type is usually
sufficient. The main point of having operator classes is that for some
data types, there could be more than one meaningful ordering. For
example, we might want to sort a complex-number data type either by
absolute value or by real part. We could do this by defining two
operator classes for the data type and then selecting the proper class
when creating an index. More information about operator classes is in
Section 11.10 and in Section 38.16.
When CREATE INDEX is invoked on a partitioned table, the default
behavior is to recurse to all partitions to ensure they all have
matching indexes. Each partition is first checked to determine whether
an equivalent index already exists, and if so, that index will become
attached as a partition index to the index being created, which will
become its parent index. If no matching index exists, a new index will
be created and automatically attached; the name of the new index in
each partition will be determined as if no index name had been
specified in the command. If the ONLY option is specified, no recursion
is done, and the index is marked invalid. (ALTER INDEX ... ATTACH
PARTITION marks the index valid, once all partitions acquire matching
indexes.) Note, however, that any partition that is created in the
future using CREATE TABLE ... PARTITION OF will automatically have a
matching index, regardless of whether ONLY is specified.
For index methods that support ordered scans (currently, only B-tree),
the optional clauses ASC, DESC, NULLS FIRST, and/or NULLS LAST can be
specified to modify the sort ordering of the index. Since an ordered
index can be scanned either forward or backward, it is not normally
useful to create a single-column DESC index — that sort ordering is
already available with a regular index. The value of these options is
that multicolumn indexes can be created that match the sort ordering
requested by a mixed-ordering query, such as SELECT ... ORDER BY x ASC,
y DESC. The NULLS options are useful if you need to support “nulls sort
low” behavior, rather than the default “nulls sort high”, in queries
that depend on indexes to avoid sorting steps.
The system regularly collects statistics on all of a table's columns.
Newly-created non-expression indexes can immediately use these
statistics to determine an index's usefulness. For new expression
indexes, it is necessary to run ANALYZE or wait for the autovacuum
daemon to analyze the table to generate statistics for these indexes.
For most index methods, the speed of creating an index is dependent on
the setting of maintenance_work_mem. Larger values will reduce the time
needed for index creation, so long as you don't make it larger than the
amount of memory really available, which would drive the machine into
swapping.
PostgreSQL can build indexes while leveraging multiple CPUs in order to
process the table rows faster. This feature is known as parallel index
build. For index methods that support building indexes in parallel
(currently, only B-tree), maintenance_work_mem specifies the maximum
amount of memory that can be used by each index build operation as a
whole, regardless of how many worker processes were started. Generally,
a cost model automatically determines how many worker processes should
be requested, if any.
Parallel index builds may benefit from increasing maintenance_work_mem
where an equivalent serial index build will see little or no benefit.
Note that maintenance_work_mem may influence the number of worker
processes requested, since parallel workers must have at least a 32MB
share of the total maintenance_work_mem budget. There must also be a
remaining 32MB share for the leader process. Increasing
max_parallel_maintenance_workers may allow more workers to be used,
which will reduce the time needed for index creation, so long as the
index build is not already I/O bound. Of course, there should also be
sufficient CPU capacity that would otherwise lie idle.
Setting a value for parallel_workers via ALTER TABLE directly controls
how many parallel worker processes will be requested by a CREATE INDEX
against the table. This bypasses the cost model completely, and
prevents maintenance_work_mem from affecting how many parallel workers
are requested. Setting parallel_workers to 0 via ALTER TABLE will
disable parallel index builds on the table in all cases.
Tip
You might want to reset parallel_workers after setting it as part
of tuning an index build. This avoids inadvertent changes to query
plans, since parallel_workers affects all parallel table scans.
While CREATE INDEX with the CONCURRENTLY option supports parallel
builds without special restrictions, only the first table scan is
actually performed in parallel.
Use DROP INDEX to remove an index.
Like any long-running transaction, CREATE INDEX on a table can affect
which tuples can be removed by concurrent VACUUM on any other table.
Prior releases of PostgreSQL also had an R-tree index method. This
method has been removed because it had no significant advantages over
the GiST method. If USING rtree is specified, CREATE INDEX will
interpret it as USING gist, to simplify conversion of old databases to
GiST.
Each backend running CREATE INDEX will report its progress in the
pg_stat_progress_create_index view. See Section 28.4.2 for details.
EXAMPLES
To create a unique B-tree index on the column title in the table films:
CREATE UNIQUE INDEX title_idx ON films (title);
To create a unique B-tree index on the column title with included
columns director and rating in the table films:
CREATE UNIQUE INDEX title_idx ON films (title) INCLUDE (director, rating);
To create a B-Tree index with deduplication disabled:
CREATE INDEX title_idx ON films (title) WITH (deduplicate_items = off);
To create an index on the expression lower(title), allowing efficient
case-insensitive searches:
CREATE INDEX ON films ((lower(title)));
(In this example we have chosen to omit the index name, so the system
will choose a name, typically films_lower_idx.)
To create an index with non-default collation:
CREATE INDEX title_idx_german ON films (title COLLATE "de_DE");
To create an index with non-default sort ordering of nulls:
CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);
To create an index with non-default fill factor:
CREATE UNIQUE INDEX title_idx ON films (title) WITH (fillfactor = 70);
To create a GIN index with fast updates disabled:
CREATE INDEX gin_idx ON documents_table USING GIN (locations) WITH (fastupdate = off);
To create an index on the column code in the table films and have the
index reside in the tablespace indexspace:
CREATE INDEX code_idx ON films (code) TABLESPACE indexspace;
To create a GiST index on a point attribute so that we can efficiently
use box operators on the result of the conversion function:
CREATE INDEX pointloc
ON points USING gist (box(location,location));
SELECT * FROM points
WHERE box(location,location) && '(0,0),(1,1)'::box;
To create an index without locking out writes to the table:
CREATE INDEX CONCURRENTLY sales_quantity_index ON sales_table (quantity);
COMPATIBILITY
CREATE INDEX is a PostgreSQL language extension. There are no
provisions for indexes in the SQL standard.
SEE ALSO
ALTER INDEX (ALTER_INDEX(7)), DROP INDEX (DROP_INDEX(7)), REINDEX(7),
Section 28.4.2
PostgreSQL 15.7 2024 CREATE INDEX(7)
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